The invention relates primarily to the field of air conditioning and in particular those HVAC systems that utilize a series of heating and cooling coils, known as a coil assembly, to transfer heat to or from the air stream in the unit. A coil assembly is really a bank of tubes, with each tube known as a xe2x80x9ctube facexe2x80x9d or may be referred to as simply a xe2x80x9ctubexe2x80x9d in this application.
The invention involves a sleeve type inner valve that works in conjunction with ports in the outer body and each of the tubes in the bank of tubes to divert a portion of the water flowing in the tubes and send it back to the outlet manifold that collects water from the entire bank of tubes. In this manner, the heat transfer capacity of the unit can be varied without having to vary the overall flow of water through the inlet manifold (albeit water flow in sections of the individual tubes is varied in accordance with the invention).
The system is believed to find its greatest use in commercial building types of applications where large heating/ac units are used to heat and cool buildings. The design of such heating/ac units results in a bank of heat transfer tubes that is fed by an Inlet manifold. In prior art the flow of water through the tubes connected to the manifold remains unblocked at all times hence, the number of passages through the bank of tubes is unrestricted. This means that when less than design volume is required, the overall flow of water at the inlet manifold is reduced which results in tubes in the bank getting uneven and disproportionate flow. This results in cycling of temperature, laminar flow, stratification and inefficient operation.
It is found that during the majority of operating hours, the actual amount of water flow through the coil is less than 25% of the calculated design flow requirement. Such units typically operate with this increment of water flowing through the tubes of the unit, much if not all of the normal day. The resulting condition (excess heat transfer capacity under part load) means that only a fraction of the tubes in the coil actually have significant water flow for the reason discussed above.
The over capacity at part load thus causes cyclic control resulting in hot and cold temperature swings throughout the day which prompts complaints from the occupants. This of course means, more building maintenance calls, perhaps more fine tuning of thermostats and discomfort for occupants prompting costly fixes designed for short term alleviation of the problem.
It is the object of the invention to avoid these temperature swings by closing off certain sections of each tube in the coil assembly when such are not needed and thus insuring that the volume of water flow through the unit is uniformly distributed by design while the effective heat transfer capacity of the entire unit varies as the demand warrants it. By short circuiting or bypassing some of the sections of the tubes in the coil (reducing the effective heat transfer surface) the same volume of water can flow through the unit but with diminished heat transfer capacity.
Since coil assemblies are used for heating and cooling they can be dedicated to one or the other or used for both. A single assembly can serve both functions where the heating and cooling medium is switched from one to the other as required to satisfy building requirements. In either case the ports can be characterized to satisfy a variety of flow requirements. A major advantage is realized in the ability to change the heat transfer capacity when a single coil is used for both cooling and heating where the required transfer surface for heating is much less than for cooling. The modulator effectively modifies the design characteristic and heat transfer capacity of the coil by changing the amount of active heat transfer surface.
The invention performs this function by means of a sleeve type inner valve that cuts off or blocks flow to a portion of each tube row in response to a control device detecting that full volume flow is not required. Thus, the invention restricts flow through certain sections of each and every tube in the tube bank when such flow is not needed and thereby minimizes the potential cycling of temperature in the unit when such flow is not restricted.
A coil modulator apparatus for use in connection with heat transfer coil assemblies found in commercial heating and air conditioning units. The coil modulator apparatus comprising an inner valve, having valve ports in the sides of the valve, that rotates within an outer housing. Apertures in the outer housing connect with each tube in the bank of tubes so that there is an aperture in the outer housing that connects with both the downstream tube section and the upstream tube section for every tube in the bank of tubes that comprise the coil assembly. Water in the coil assembly, flowing in the upstream section of a tube, thus travels out of the upstream section and into the coil modulator when the modulator is opened and in use.
All or a portion of the water that collects in the modulator then flows back out of the modulator and into each of the downstream sections of every tube in the coil assembly. Another portion of the water in the modulator is diverted from the bank of tubes so that it flows out of the bypass tube of the modulator and directly back to the return manifold of the coil assembly unit. Rotation of the inner valve of the modulator varies the effective flow of water flowing through the downstream section of each tube in the assembly. Flow is varied in accordance with the heat transfer needs of the building.
Thus the use of the coil capacity modulator means that water flow to the coil supply manifold need not be varied to meet the different needs of the building. Heat transfer capacity is varied by diverting a portion of the water out of each tube in the bank so that the overall volume of water in the upstream section of the tube does not change but the volume in the downstream section does. This results in an equal flow or designed volume of water in every tube in the coil assembly. The overall volume of water flowing in the inlet and outlet manifolds will depend on the location and characterization of the inner valve ports (see FIG. 10).
It is an object of the invention to provide an improved heat transfer unit that maintains relatively high flow in the upstream section while modulating the flow rate in the individual downstream sections of each tube in the coil assembly.
Another object of the invention is to provide a modulator for varying the heat transfer capacity of the coil in an heating/ac unit without having to vary the overall volume of water flowing through the coil for freeze protection when used for heating and to provide chiller flow protection when used for cooling.
Another object of the invention is preventing the cycling of building temperatures that result when the design heat transfer capacity of the coil assembly exceeds the amount of heating or cooling necessary to meet demand (over capacity at part load). This is the condition that exists in coil applications when the volume of water to the supply manifold is decreased to effect a reduced heat transfer and the active transfer surface area remains constant.
Another object of the invention is to eliminate stratification by uniformly distributing water through selected tubes when the coil is operating under reduced load and the flow rate is significantly below design conditions.
Another object of the invention is to provide more efficient air conditioning of buildings by maintaining uniform flow through a portion of each row in the assembly for freeze protection while reducing or stopping flow in another section of the tube row to reduce total heat transfer capacity of the unit.
Another object of the invention is to increase the heat transfer capacity of the coil assembly in reverse proportion to the flow rate to maintain a relatively high temperature differential by characterizing and locating ports in the inner valve to reduce total volume by closing upstream ports of selected tubes and opening ports in the modulator to allow flow from the modulator through selected downstream tubes. The result is reduced flow and increased heat transfer to raise water temperature going through the coil to improve chiller efficiency when the system is operating at part load in the cooling mode.
Another object of the invention is to minimize the need to employ pumps to ensure uniform distribution of water during periods of low demand and when two or more coils are used in parallel. By varying all tube openings discretely the coil capacity modulator ensures uniform distribution in all active tubes and minimizes the problem associated with laminar flow. The coil capacity modulator facilitates maintaining a relatively high and uniform tube velocity at part load compared to prior art.
Other objects of the invention will become apparent to those skilled in the art once the invention has been shown and described.